Isolation voltage and signal path for industrial BOMs
The 4N28M is a 1-channel DC-input optoisolator with a transistor-with-base output, rated for 4170Vrms isolation between input and output sides. That isolation rating suits it for breaking ground loops and protecting low-voltage logic on the secondary side in motor drives, PLC digital inputs, and power-supply feedback paths. Typical turn-on and turn-off times of 2 µs each limit the useful switching frequency to roughly 100 kHz — adequate for 50/60 Hz line synchronisation, relay coil drive, or slow serial isolation.
Temperature range and output drive limits
Maximum output voltage is 30 V, and Vce saturation is 500 mV max at rated current — the output can pull a 5 V or 24 V logic input low with margin. Forward voltage typical is 1.18 V at 10 mA, and the LED can be driven up to 60 mA continuous.
Active lifecycle — no immediate obsolescence risk
For BOM planning, this means the part can be specified without a near-term requalification trigger, though sourcing should still be confirmed per order to avoid allocation shifts.